//Calling Code for VM to pass message box delegate
Func<string, string, MessageBoxButton, MessageBoxImage, MessageBoxResult> messageBox = (msg, caption, buttons, image) => MessageBox.Show(msg, caption, buttons, image);
 
//pass above variable to VM
 
//Usage of message box delegate variable inside VM
MessageBoxResult = messageBoxinVM("Test Message", "Test Caption for Message", MessageBoxButton.YesNoCancel, MessageBoxImage.Question);